Cladding and wainscoting of cold internal walls

gutovicky

Hello all,
May I ask another little question...  before I launch myself into this wall-insulating project...
It's a small point, but I don't want to make a silly error..

My question is: 
When insulating the inside of an external wall (for example, using FreeBear's "wooden battens and foil-faced insulation board method") should the insulation go all the way to my bungalow's floor level [concrete slab]
OR should I leave a small gap at floor level?

Thank you, Vicky

FreeBear

Floor to ceiling. If you leave a gap at the bottom or top, a cold spot will form and could attract condensation.

On the walls that I have done here so far, the insulation extends below the floorboards and also in to the loft space above the ceiling. As the floor is suspended timber, going below the floor level is a doddle. Insulating above the ceiling, not so easy unless the ceiling is coming down.

With a concrete slab, taking the insulation below floor level is just way too much effort for a negligible gain.

Apodemus

FreeBear said:

FreeBear said: If you want sockets (or switches) on the wall(s) you are insulating, it is worth putting some thought in to where you want these items located before starting work. Put up your first layer or two of Celotex, and before the last 25mm layer goes on, fix some 35mm deep back boxes to the wall

Tip - A serrated kitchen knife is an ideal tool for cutting the insulation. A clean cut with minimal dust. I have a Kitchen Devil about 150mm long that I use.

...or a wheel-type pizza cutter!  Even less dust than a serrated knife!  But only for cutting the sheets, you still need the knife for the back-box holes.

chris_n

Best to leave a small gap at the bottom and top, just enough for a spray foam application nozzle. An alternative is to cut at a slight angle to provide space for spray foam. It is unlikely that you would be able to cut so accurately that there would be no gap at some point. If you are putting any insulation, even laminate underlay on the floor put this underneath the wall boards before foaming too.

gutovicky

Thank you for the tips!

Yes, once battens & insulation boards are fixed, I can see myself squirting a little [expanding] foam along the line where floor meets wall.

In any case, there’s a narrow channel along this line....
The channel goes under the (butt-edge of the) internal rendered/plastered surface of the wall (approx 3cms) until you reach the brickwork - this is normal, right?    [in other words, the rendering/plastering inside the room does not make contact with the floor slab].

Doesn’t this gap/channel need filling in?  - with the [expanding/insulating] foam…? 

chris_n

I would fill it.

FreeBear

gutovicky said: Yes, once battens & insulation boards are fixed, I can see myself squirting a little [expanding] foam along the line where floor meets wall.

In any case, there’s a narrow channel along this line....
The channel goes under the (butt-edge of the) internal rendered/plastered surface of the wall (approx 3cms) until you reach the brickwork - this is normal, right?    [in other words, the rendering/plastering inside the room does not make contact with the floor slab].

Get yourself a couple of cheap foam guns - https://www.ebay.co.uk/b/Expanding-Foam-Gun-in-Other-Diy-Materials/20594/bn_7022609068 - along with a can of gun cleaner.

Used with "gun grade" expanding foam, it is much, much easier to lay down a precise bead just where it is needed. Keep the nozzle clean (a squirt of gun cleaner helps), and you should get plenty of life out of the gun. If you take a can of foam off the gun, screw the gun cleaner can on and pull the trigger to clean out the internals.

A photo of this "channel" would help to identify its purpose - Depending on what it is for, it might want to arrange so that there is easy access to it.

plumb1_2

Better to leave a 20mm gap from the concrete/screed floor. If you get sort any of leak/damp the insulation will just soak it up like a sponge. 

gutovicky

...Not sure I explained myself very well on that last question....  sorry folks.

But I'm with you there plumb1_2    -  I should keep the floor slab isolated from the rendered surface of the walls (whether insulated or not...).

I have one more question on this topic - then I'm done!!

I may be overthinking this - but is there any risk that the rendered surface of the internal walls that are NOT insulated will leak cold/warm air, even moisture, into the rendered surface of those walls that ARE INSULATED?
[Think, for instance, of the wainscoting I wanted in the dining room - where the lower half of the wall is insulated + boarded, and the upper half of the rendered wall is left uninsulated].

In other words, could I be creating lots of cold bridging by partially-insulating a rendered room?
[Like I say, this may be a stupid question, forgive me...].

Thanks again for your time, Vicky

FreeBear

Personally, if there is any potential of damp in the floor slab. I'd put a length of this down on the concrete & fold it up the wall - https://www.screwfix.com/p/capital-valley-plastics-ltd-damp-proof-course-black-30m-x-150mm/78665 (perhaps a wider roll). This will stop any moisture wicking up into the insulation and allow you to go right down to floor level. So no cold spots.

And I bet there will be loads more questions, there always is